Solvent fractionation of refined glyceride oils



Jan. 30, 1951 s. E. FREEMAN ET AL y 2,539,661

soLvENT FRACTIONATION oF REFINED GLYCERIDE oILs Filed oct. 15, 1947 91T TURA/EW Patented Jan. 30, 1951 UNITED STATES PATENT OFFICE SOLVENT YFRAC'I`.I.()1\T ATION 0F REFINED GLYCERI-DE OILS Application October 15, 1947, Serial No. 780,060

13 Claims. 1

The present invention relates t a method of separating oils composed essentially off glycerides of a mixture oflngher fatty acids which are, distingushed from each .other primarily by the d e.. grecsv of or the molecular .arrangement ot the double bonds in the hydrocarloon 'chains into fractions upon .the basis of the uhsatulatOli v0f the. acid components.

.One object, yof the invention :is to 'provide o process of fractionating `oils composed O giroerides of relatively saturated and unsaturated higher fatty acids Which `can be efficiently op. erated by continuous counter-current methods to. .obtain from a drying or semi-drying Aoil a relatively large proportion of oil especially adapted to use in paints and other coating media.

n. .second object to .ob-tain .from a drying or semi-.drying oil a .fraction which is rich lin the more satnrated more solid, components of tho oil.-

A third object of the invention is to providey a process. of rractionating oils .of the foregoing type in which fractionation of glycerides uponv the vbasis of degree-of unsaturaton can be. effooted Vcountenzurre,ntly in asinygle` step extraction,

lA, fourth object is to provide a process of. the foregoing, typeA `that can be. operated Without diffnoulty from' ernulsioation .of the oilv and' the;

polar solvent.

Those andl other obieots. willl be. apparent from consideration of. the, following. spooioaf tion. and the .appended danno..

It h aslong been recognized 'that glyceride oils and. notably oils of the drying or semi-drying type Werel composedV mainly of the glycerides of a' plurality of higher fatty acids of varying degrecsY of unsaturation. v'The various iat-ty acid components of the glycerides d-iier vin proportion with dilerent oils and are 'in-uenced. by such factors as climate, variety and so forth; However, soybean oil is a typical example .of an oil which has drying properties butstill, in its natural state .isnpt .entirely satisfactory for vuse as a, coatingl composition.

.Soybeanoil is a l'mixture of elyoorides of various fatty acids in` which the fatty acids are in the following proportion.:

Per cent.

arachide acid.

.-Thepercentages designated are based upon.

' the total .of the. acids the esters. of which 4are.

present in the glycerides. It; is a characteristic of the glycerides containing such mixture .of fatty acids 'that .the acid radicals are, relatively uniformly mixed in the glyceride molecules.

" That is, each gylceride molecule .will contain .a

radical vand a linoleic acifd radical.

plurality of different acid radicals. For exam ple, the gylceride molecule may contain one; oleic acid radical, one. palmi-tic or stear-ic acid There. will y be presfnt also various other rpossible `combinations of the different acids. and there may be present small amounts of the triglycerides `of single acids.. These facts .are established in Thorpes Dictionary `of Applied Chemistry, yol` ume 4, pagos 8l and .82 y(Lith edition).

radicals are susceptible of rapid dryingwhen' spread as 'lms. These impart tof-the o'iI 'drying-7 oharacteristics which Vhave `heretofore led to. considerable use Aof vthe oils to replace a portion ,y of the linseed oilin paints and varnishes. However, the natural oil is comparatively ,slowin drying and is not customarily employed as the solefdry-ing oil component of a paint or varnish.

It has heretofore been proposed to subjectl a glycerid'e oil such as soybean oil composed of;y

" drying and non-drying glycerides to a process of fractionationA in order to obtain a portion of*` superior drying Yproperties and atv the same time` to Yobtain non-dryingfractions of superior value.

for other purposes such as use in food products,A

` e. g., shortenings, salad' oils, butter substitutes or ,the like.

It .has further been proposed to fractionatei elvooride oils such as lilrlsfeeciv oil ahdlsoybean oil'.-

. and other oils comprising mixtures of' glyceridies of relatively highly saturated and. relatiyely highly nnsaturated` .acids .into fractions.- upon. thebasis ofv they degree .of yunsaturati'on of .acid .radiev` cals in the glycerdes. by means .of selective sol-...

vents having .a greater taffinity for the .more'unsaturated gllioerides. `Solvents suitabley for the, purpose in. general are.v of. the class. known as This typeof process is broadlyv disclosed in S. Patent. 2,200,391 to.. Stephen... E. Freeman. Thepatent.. lists a large. num-ber;

polar solve nts.

plication of which suitability of a given solvent can be predicted with a considerable degree of accuracy. By application of the process as described in the patent, oils have been successfully fractionated upon an extensive scale. However, under some conditions certain diiiiculties have been encountered in the operation of the process. One such difculty involves a tendency of certain of the oils, notably crude linseed and crude soybean oil, to form emulsions with the solvent employed in the extraction system.

One of the most convenient solvents for use in the process comprises furfural which is relatively abundant and inexpensive and which has many other characteristics rendering it valuable for use in the process described in the patent. However, in the extraction of crude linseed oil or crude soybean oil with furfural in order to obtain relatively saturated and unsaturated fractions much difiiculty from emulsication has been encountered. When emulsication occurs, the oil and the solvent become so intimately associated that separation into phases cannot be attained within a reasonable period of time. Therefore, the volume of oil that can be put through a given piece of apparatus is greatly reduced. Countercurrent extraction methods then become impracticable. Perhaps batchwise operations, in which portions of emulsied oil and solvent could be left standing for long periods of time would be operable but these in general are not eicient or economical.

The present invention involves the discovery that the emulsiication of the glyceride oils with selective polar solvents such as furfural in the fractionation of glyceride oils is largely due to the presence of certain non-glyceride components Yof the oil. These components are usually termed gum constituents. It has now been found that if these are removed or their concentration is sufliciently reduced, before the oil is subjected to extraction with the polar solvent, the difficulties with emulsication are substantially eliminated. g In order to obtain an oil which will not emulsify when it is countercurrently extracted with furf'ural or similar solvents, the oil may be subjected to alkali treatment known as refining, or in `some instances, washing with water is subcient. The oil when so treated can be put through an extraction column without appreciable tendency to emulsify with furfural.

TheV techniques of alkali refining and water washing have heretofore been developed for other purposes and are not here greatly departed from except in the subsequent application of solvent extraction to obtain the portions which are of especial interest to. the paint and varnish industry from those portions of particular merit for use as food fats( The rening and washing technique is well understood by those skilled in the art and usually involves considerable degree of personal experience upon the part of the practitioners. The broad technique, however, has been delineated in various textbooks and publijcations available to the art. One such publication'is 'Industrial Oil' and Fat Products, A. E. Bailey, published by the Interscience Publishers Incorporated of New York, .1.945. Probably the simplest technique which can be employed to obtain an oil suitable for the purpose of the present invention involves simple deguniming by heating the oil in the presence of water in order to precipitate out phosphatides, protein and gummy or mucilaginous substances. This technique isdescribed on page 501 of the text as follows:

Certain oil impurities such as phosphatides, proteins or protein fragments, and gummy or mucilaginous substances, are soluble in the oil only in an anhydrous form, and can be precipitated and removed if they are hydrated. The hydration and removal of phosphatides from soybean oil has been described previously in connection with the solvent extraction of soybeans. Other. vegetable oils, and particularly corn and cottonseed oils, are also sometimes subjected to a similar degumming process prior to alkali rening, in order to reduce the refining loss.

The water washing or degumming process is similar to continuous alkali Arefining except that warm water is used in place of the alkali.

The art of degumming by precipitation of the phosphatides and such like constituents by vwater as well as alkali refining are discussed in numerous other texts including Vegetable Fats and Oils by Jamieson, Second edition, copyrighted 1943 by the Reinhold Publishing Corporation, 330 W. 42nd St., New York, N. Y., pages 206` and 207; Fats and Waxes, by Hilditch, copyrighted by D. Van Nostrand Company, 8 Warren St., New York, N. Y., 1927 (see pages to 197 inclusive).

In the practice of the present invention a glyceride oil which has been suitably rened to eliminate the tendency to emulsify, characterizing raw or natural oil and comprising a mixture of glycerides of fatty acids of varying degrees of unsaturation is subjected to fractionation into relatively highly saturated and relatively highly unsaturated portions in accordance with the technique described in the aforementioned U. S. Patent 2,206,391.

The oils contemplated as being within the purview of the invention include linseed oil, cottonseed oil, soya bean oil, corn oil, fish oil, whale oil and the like appropriately rened, but degummed or refined soybean oil and linseed oil are particularly contemplated because with the crude oils from which they are derived, emulsification is especially severe. Moreover, they are composed of glycerides of fatty acids-of such nature that when properly fractionated, portions of exceptional value for use in coating compositions are readily obtained and at the same time, fractions of especial value for use in the preparation of food products or other uses are obtained as ranates.

The solvents disclosed in the U. vS. Patent 2,200,391 are contemplated as being Within the purview of the present invention. However, furfural, all points considered, seems to be the most practical. Other very satisfactory solvents include methyl acetoacetate, ethyl acetoacetate, acetonyl acetone, nitrometharie, nitroethane, methyl cellosolve, methyl formate, methyl levulinate, glycol diacetate.

The technique of extraction is susceptible of considerable variation but may be outlined broadly as follows:

.The solvent should be employed in a range of 3 to 30 parts by volume per part of oil to be treated. The preferred range is approximately within the limits of 6to 15l parts per part of oil treated. However, these limits are set more by the economics of solvent evaporation than by behavior of the solvents with respect to the oil to be treated.

It will be apparent that the temperatures of operation will vary for different solvents, the proportion of solvents and with the oil to be treated by given solvents; For example, soybean oilwhich has been rened may be extracted with very satisfactory results within a temperature range of about 109 to 111 F. Variation of a few degrees in either direction is contemplated. In any event, the temperature at which a satis- Yfactory proportion of extract is obtained can be ,determined quite readily. The system should be so operated that the oil is but ,partially miscible with .the solvent employed. It will be apparent that if the temperature is raised unduly, all of the oil or substantially all of it will go into vsolution; under which conditions no appreciable fractionation is possible. If the temperature is too low of course only small extract fractions consisting largely of by-products will be obtained and .for most purposes the process is undesirable.

.Assuming that soybean oil is to be treated, 'Sthe Vbest temperature is that at which a fraction of about 40 to 75% of the oil passes into solution as kan extract. When the system is so operated the extract will be greatly enhanced in iodine value. Ordinary soybean oil has an iodine value of approximately 130 to 138. These improved fractions have iodine values of approximately 150 to 156 or 157. Although these values still are substantially Aless than those of ordinary linseed foil., they dry almost as fast as the latter. It probably is practically impossible to obtain an appreciable fraction from soya oil of an iodine value corresponding to that of linseed oil (about 180) because of the uniform distribution of the saturated and but slightly unsaturated acid radicals in the glyceride molecules. However, this fact is `not very important since the extract oil dries nearly as well and in certain respects even better than linseed oil.

A suitable embodiment of apparatus for use in the practice of the invention is diagrammatically illustrated in the single ligure of the Adrawings in which like numerals refer to like parts throughout.

The apparatus as shown includes a vertical column lil in which the vextraction of the 'oil with the polar solvent may conveniently be conducted. This 4column is packed with vRaschig rings, Berl saddles 4or other packing designed to assist yin obtaining thorough contact of oil yand solvent medium. It may be of any convenient length but preferably it is 70 or more feet in length. Relatively long columns are especially desirable for the fractionation of soybean Yoil since the latter appears to require considerable .stages .of contact with the polar solvent in order to attain equilibrium conditions. The column may be 150 ft. in length or even longer. There appears to be no particular upper limit'of length other than such as may be imposed by the costs of construction and such factors.

Contiguous to the column are disposed a container I l for the storage of an appropriate amount of the oil to be extracted and a container I2 for the storage of polar solvent such as furfural. A third container i3 is -optional and vis for 7the storage of naphtha'which may be employed in admixture with the vpolar solvent as .it is fed into the extraction column l0. It is to be reiterated that the use of naphtha as an adjuvant is optional and may be dispensed with if so desired. "Such container would be joined to column I Vby line Hl Yhaving a preheater 14a.

The lfeed of oil to vthe vcolumn -IEl -is eiected at some intermediate point and may as `shown in the drawings, bei near the middle of thecolumn but considerable variation in veither direction admissible. t may, lfor example, occur at any point V'between the lower quarter and the upper quarter. Feed of oil to the column is effected through a conduit l5, having a distributor head Ia in the column. yA `portion of line i5 may be coiled as shown at I6 and disposed in a preheater shell il. Fluids designed to bring .the glyceride oil to appropriate temperature are circulated through the shell by means of inlet con duit |-8 and outlet conduit l 9.

A similar arrangement is provided for the control of vthe temperature of and 'the feeding of selective polar solvent into the Zone near `the top ofthe column. A rfeed line`22 from container 4I2 yfor this purpose is indicated diagrammatically in the drawings and the feed Vis Aconducted through a temperature conditioning apparatus which "may function either as a preheater 23 or as acoc'ler as climatic conditions or the nature of the oil may dictate.

In order to maintain the desired temperature within the column or to obtain a suitable gradient of temperature between the top and bottom, suitable temperature conditioning devices may be provided. Such devices would include jackets (not shown) disposed about the columnand being provided with suitable conduits for circulation or a temperature conditioning medium.y For large installations, external hea-t exchange elements are more suitable. 'Such devices are illustrated at 24 and 2ev in the drawings and may .include `coils 2l and 2'8 lappropriately .connected by means fof conduits 21a and 28a with the column |29 pso that portions of oil and ysolvent may be drawn oi heated or cooled and returned to the column. Any convenient number of coils may be so provided. The coils are installed in jackets or shells 29 and 3i! which conveniently are provided with inlets 3l-32, and outlets 33--34 for the circulation of a liquid medium which maybe either hot or cold vas conditions may require.

It will 'be apparent that vthe glycerde oil, .after introduction into the column is contacted yinti i mately with the downwardly iiowing solvent introduced slightly below the top of lthe column through `the line 22. The raffinate oil freshly washed Awith the solvent of highest purity'and saturated with a small amount of the solvent is drawn off at the top of the column above the point of :inlet of selective solvent through lineielll. vThis raflinatefraction of course comprises Ythe relatively more `saturated glycerides especially suitable 'for use in food products. Raiiinate solution passing through line 3 6 may conveniently be subjected to Adistillation in -a still 38 of conventional design for .the removal of the major portion of the solvent. The raffinate oil is drawn off through line 4| and maythen be passed .through a steam stripper 42 for the 'complete and thorough removalof any solvent which may be dissolveditherein. The finished raflinate is drawn off through line 143. Solvent 'from the oil as obtained in the still 3.8 is drawn off through line 44, preferably in vapor phase and is ycondensed in a suitable condensing apparatus 46. It may be passed through line '4.3 tothe container |2 ior'reuse in the system. Such recycling -is `optional but usually is dictated aby the economics 'of operation.

Extract solution of the moreunsaturated'glycerides dissolved in the polar solvent is drawn off from thebottom ofthe column through the line 49.

All of vit'may be passed through a still 54 for fthe removalof solventfand the recovery .of

the oil dissolved therein. The solvent in vapor phase passes oi through line 55 to a condenser 56 in which it is recovered and then returned through line 51 and 48 to storage container I2. The extract oil comprising the highly unsaturated glycerides passes oi from the still through lines 58 to a second stripper 59 in which it is subjected to a steam distillation operation in order to eiect more thorough elimination of any solvent contained therein. The solvent free extract oil may pass to storage through line 60 or if it is desired a portion of the stripped oil may be fed as reux to the bottom portion of column I through line 60A.

In some instances the iodine value of the extract, as obtained from the system may be improved by recirculating a portion of the extract oil from which the solvent has been partially or completely removed. The amount of oil so reuxed will vary with the iodine value desired in the extracted oil and the economics of operation. In general, a reflux of .l to parts of extract oil per part of oil treated is contemplated. Preferably, this refluxed or recirculated portion of the oil is introduced near but above the bottom of the column and the point at which extract solution is withdrawn. For purposes of maintenance oi such reux, a portion of extract solution may be drawn off from the line 49 through a line 6I and is then passed through a still 62 similar to the still 54 for evaporation of solvents. The solvent from this portion of the oil, of course, is recovered, being taken off through a line 63 and condensed in condenser 5S. The condensate is returned to the container I2 through lines 51 and 48. Usually the reflux fraction will be reduced to at least 50% solvent in the still 62. The reuxed portion of oil is drawn oli through line 61 and may, if desired, be passed through a temperature conditioning device 68, e. g., a coil in which the temperature is brought to appropriate Value for introduction into the column. The reux fraction passes from the device through line 69 to the distributor head 'II within the column slightly above the bottom thereof.

If prepared, a reiiux of naphtha from a container I3 may be substituted for all or a portion of the reflux of oil into the bottom of the column `Ill. This reflux should not be so great as to impair the yield of extracted oil in the polar solvent and preferably is Within a range of .lA to 2 parts based upon the feed oil for this purpose.

In order to maintain the flow of liquids in the system, pumps may be required. The positioning of and the number of these pumps Will depend upon the relative positions of the various pieces of apparatus which of course will be dictated by local conditions and the judgment of the engineer designing the apparatus. Valves for shutting off the ow of liquids or for proportioning the flow of liquids throughout lines or conduits are also desired. These may be introduced in any of the lines. Some of them are indicated in the drawing by the letter V.

In the operation of the apparatus shown and described, the glyceride oil, e. g., soybean oil which has been subjected to a refining operation such as degumming by heating in the presence of water and/or alkali refining is passed into the column I0 through the line I5. Simultaneously, a selective polar solvent, e. g., furfural is passed in at the top of the column through the line 22. If desired, 1% up to 15% of naphtha may be added to the oil before extraction though 8 this is not an essential feature of the invention. Under some conditions, separation of the phases is promoted thereby.

The ralnate oil passing off through the line 36 is subjected to distillation in the still 38 to remove solvent such as furfural which is condensed in the condenser 46 and may be recycled. The railnate oil comprising glycerides of relatively low degree of unsaturation, e. g., 110 or thereabouts may be further steam stripped in the stripper apparatus 42. The resultant product is very suitable for use in food products. Of course, it can be hydrogenated in order further to reduce the iodine value thereof and thus to improve the hardness of the product. The products obtained by hydrogenation of raflinate extract herein disclosed is of superior value from the standpoint of stability, taste and such like factors as compared with similar products obtained by hydrogenating the whole soybean oil.

The extract phase passes out through line 49 and comprises most of the solvent introduced into the system as well as the more unsaturated glycerides dissolved therein. All of it may be passed through the still 54 to remove the major portion of the solvent after which it is completely stripped of solvent in the stripper 59. Of course, the solvents so recovered may be returned to the system. The extract oil will have iodine value above 140 and usually above 150.

If it is desired to increase the iodine value of the extracted oil, a reflux portion is taken oil` through line 69 and is a certain portion of the extract solution partially or completely freed of solvent in still S2. A reiiux could be taken from the oil passing out of still 54 thus eliminating still 62. However, greater exibility of operation is attained with two stills. The reux is returned to the lower portion of the column II) through line 69. The amount is within a range oi .1 to 5 volumes per volume of oil from container II.

If desired this reux oil may be admixed with or replaced by a reux of naphtha from the container I3. The proportion may be 0.1 to 2 volumes per volume of oil from container II. In

' 'any event, the amount of naphtha is maintained sufficiently low that there is no appreciable separation of a separate naphtha phase in the system.

The following constitutes specific examples illustrating the operation of the apparatus as herein shown and described.

Example 1 [Oil used, alkali-refined linseed oil. Solvent used, urlural]v Ratio-Parts Conditions of Operatlon Gal/hr. per Part Feed Oil Oil feed to column i Ratio-Parts Conditions of Operation Parts/min. per Part Feed Oil Oil feed to column 20 Solvent to column 166 8 3 to l Reflux oil feed to column 22 l 1 to 1 Column temperature: Top, 109 F. Bottom, 111 F.

Per Cent Products Yield I. V. Llne Extract 57. 3 155. 0 60 Ranate 42. 7 110. 4 43 Original oil. 136. 5 14 Example 3 [Oil used, water degumrncd soya oil. Solvent used, furfural] Ratio-Parts Conditions of Operation Parts/min. per Part Feed Oil Oil feed to column 20 Solvent feed to column 166 8.3 to 1 Reflux oil feed to column 22 1.1 to l Column temperature: Top, 109 F. Bottom, 112 F.

Per Cent Products Yield I. V. Lino Extract 58. 8 156. 2 R'iflnate 4l. 2 111.6 Feed oil 136. 6

Eample 4 [Oil used, refined soybean oil (water degumrned). Solvent used, furfuml (naphtha sat.)+a naphtha ol 8 to 1l carbons.]

It will be apparent to those skilled in the art that the embodiments of the invention herein shown and described are by way of illustration. Numerous modifications may be made therein without departure from the spirit of the invention or the scope of the appended claims.

We claim:

1. In a process of treating a natural glyceride oil to separate therefrom a portion which is substantially enriched in one or more components of the natural oil, the steps which comprise removing the gum from the natural oil, then extracting out said portion by countercurrently flowing furfural through the oil, the resultant system `of oil and furfural being maintained at a tempera- .ture below that of complete miscibility of the two.

2. A process as dened in claim 1 in which the oil treated is soybean oil.

3. A process Tof .treatngafnatural glyceride oil containing break constituents,. a portion- `of glycerides of fatty acidsI of a high degree o'f'unsaturation and being adapted to air dry when spread as a film upon Aa surface to form a hard coating and a portion of glycerides of fatty acids of a low degree of unsaturation and having but slight capacity for air drying, which process comiprises, refining said oil to remove said break constituents and then countercurrently flowing the oil through a body of furfural at a temperature below that of complete miscibility of the oil and the furfural, but sufciently high to remove a substantial fraction of the more unsaturated glycerides as a furfural extract and separating the furfural phase from the glyceride phase and evaporating off the furfural from the extracted glycerides.

4. A process as dened in claim 3 in which the oil treated is soybean oil.

5. A process as defined in claim 3 in which the,

oil treated is soybean oil and is in a ratio of onev volume to 3 to 30 volumes of the furfural.

8. In a yprocess of obtaining a drying oil suitable for forming coating compositions, the steps which comprise subjecting soybean oil which has been pre-treated to remove break, to extraction lby flowing furfural into an upper portion of an elongated extraction zone flowing the oil to be extracted into the same zone at a point below the point of introduction of furfural, removing the soybean rafnate oil at the top of the zone and removing furfural containing said drying oil as fraction in solution at the bottom of the zone and evaporating the furfural.

9. A process as defined in claim 8 in which a portion of extracted oil, after removal of at least a part of the solvent is reintroduced into the eX- traction system at a point below that of introduction of the solvent.

10. A Iprocess as defined in claim 8 in which the oil treated is soybean oil, furfural ratio is in a range of 3 to 30 volumes to 1 volume of oil, and the temperature is adjusted to extract out in the furfural phase 40 to '75% of the total oil.

11. In a process of treating soybean oil to separate therefrom a portion which is substantially enriched in a component of the natural soybean oil, which process comprises the steps of alkali refining soybean oil containing break constituents, then extracting said alkali refined oil by eountercurrently iiowing furfural therethrough, the resultant system of oil and furfural being maintained at a temperature below that of complete miscibility of the two, separating the resultant furfural phase from the oil phase and evaporating the furfural to obtain said portion.

12. IThe steps as defined in claim 11 in which the soybean oil is maintained at a temperature sufficient to extract out 40 to 75% of the oil in the furfural phase.

13. A process as defined in claim 11 in which y the furfural is maintained in a ratio of 3 to 30 volumes per volume of oil.

STEPHEN E. FREEMAN. STEWART W. GLOYER.

f (References on following page) REFERENS CITED OTHER REFERENCES The following references are of record in the Bailey, Ind. Oil and Fat Products (1945),Inter le of this patent: scerlce Pub., Dp. 501-3, 653-7;

UNITED STATES PATENTS 5 hollrlsaftnuer, Fats and 011s (1944), Rein- Number Name Date Klensmith et a1., Ind. 8: Eng. Chemistry, June 2,200,391 Freeman 1-- May 14, 1940 1943, page 674. 

1. IN A PROCESS FOR TREATING A NATURAL GLYCERIDE OIL TO SEPARATE THEREFROM A PORTION WHICH IS SUBSTANTIALLY ENRICHED IN ONE OR MORE COMPONENTS OF THE NATURAL OIL, THE STEPS WHICH COMPRISE REMOVING THE GUM FROM THE NATURAL OIL, THEN EXTRACTING OUT SAID PORTION BY COUNTERCURRENTLY FLOWING FURFURAL THROUGH THE OIL, THE RESULTANT SYSTEM OF OIL AND FURFURAL BEING MAINTAINED AT A TEMPERATURE BELOW THAT OF COMPLETE MISCIBILITY OF THE TWO. 